sfinae examples started

#include <type_traits>

#include <iostream>

// SFINAE test

// source: https://stackoverflow.com/questions/257288/is-it-possible-to-write-a-template-to-check-for-a-functions-existence

template <typename T>

class has_helloworld

{

    typedef char one;

    struct two { char x[2]; };

    template <typename C> static one test( typeof(&C::helloworld) ) ;

    template <typename C> static two test(...);

public:

    enum { value = sizeof(test<T>(0)) == sizeof(char) };

};

class A {

public:

	int helloworld() const { return 42; }

};

class B {};

template<typename T>

typename std::enable_if<has_helloworld<T>::value, int>::type

f(const T& t)

{

	return t.helloworld();

}

int main()

{

	A a;

	std::cout<<f(a)<<"\n";

	//B b;

	//f(b);

}